This invention relates to a surgical cable loop connector which is typically used for the securance of broken bones together, serving as an implant for use in bone surgery.
In orthopedic surgery where severe breaks of bones have taken place, or in reconstructive procedures on bones, for example reconstructive hip procedures or the like, a permanent cable implant is provided to hold bone portions together. For example, during a total hip replacement, press-fit femoral components are inserted into the canal of the femur, resulting in an extremely tight fit in some cases. Seating of these press-fit components has been shown to induce large hoop stresses in the proximal femur, which can result in longitudinal cracks. Thus, in the prior art, a cerclage cable system is provided to apply a counteracting compressive hoop stress, which prevents crack formation and/or propagation.
The existing methods of bone fixation in conditions such as the above include the use of plates and screws, monofilament wire, and cable and crimp systems. Failure of single strand wires due to fracture or loosening has been reported as being quite common. Plates and screws are also provided to attempt to reduce spiral, longitudinal and butterfly fractures, but such an expedient is not very successful with long breaks or where there are multiple bone fragments. Also, too many plates and intrusive screws tend to weaken the resulting bone union.
Existing cable systems of the prior art are bulky and stiff. Also the cable is hard to work with, and the crimp that is used requires special, cumbersome tools for tensioning and crimping. Likewise, the crimping process in many prior art systems is difficult, and must be learned to be effective.
Also, prior art cable loop connectors have exhibited a problem of bone necrosis in areas where the connector contacts the bone. An additional problem of such cable loop connectors is the possibility of slippage along the shaft of the bone after implantation.
Furthermore, with prior art cable loop connectors, the cable as it is implanted may exhibit a sharp angled turn of a few degrees at the point where it exits from an aperture in the cable loop connector, because of the relative position of the bone and the connector, and the direction of the cable passage holes in the connector. This creates a point of focused stress against the cable which can, over time, result in failure of the cable.
Also, in prior art cable loop connectors, the process of crimping to secure the cable loop is a fairly complex one, and which is easily done in improper manner. By this invention, an essentially foolproof technique of cable securance is provided.
Additionally, the cable loops that are provided by this invention may be cable loops which extend less than 360.degree. about a bone from securance point to securance point and occupy a plane transverse to the bone. In the pertinent prior art, the cable loops provided by the prior art connectors are more than 360.degree., with portions of the looped cable passing by other portions thereof in a spiral manner. This can create an undesirable torsion as such a prior art cable loop is tightened with a connector, which torsion can be eliminated by this invention.
Also, the cable loop connector of this invention is basically foolproof as to which side should be placed against the bone. In prior art systems, errors can be made with respect to that issue. Also, by this invention, securance of the cable may be performed with a single operation using a common hex head screw driver or other simple tool. To the contrary, in the analogous prior art systems two crimping steps must be provided with a special, high cost crimping tool.